Heat treatment of garnet abrasive



Patented 15, 931

Enwnv com, or cnrcaeo, rumors, Ass renon To move. m comm, or

cnrcaeo, rumors, A CORPORATION or rumors R Drawing.

' Crushed garnet, particularly the almandite and rhodolite varieties, have beenin use to' an increasing extent as an abrasive bonded to the'surface of fabrics such as paper 'and o cloth by means of glue or other suitable ad-' hesive, both in what is known as closed and open coat; generally speaking, the former for working hard wood and the latter soft wood and other substances.

It has been suggested that the capillarity of crushedabrasives, includinggarnet, may .be improved and thebonding action of, the glue or other adhesive maybe enhanced by heat treatment at low temperatures of from 0., whereby to drive off the moisture and other surface impurities, this heat treatment being .at' temperatures not crushed garnet be roasted in a suitable furnace at temperatures of from 400 to 950 C.

1 for a period of from three to sixteen hours, the physical and chemical. properties of the ner and to a remarkable degree. a The fracture is improved, the grains change in color to-adeeper red,"glist.en. as if wet, assume metallic luster, tougher and sharper to the feel, the abrasive qualities being greatly improved.

An analysis indicates that, as compared "with the untreated garnet or garnettreated ferrous form converted into the ferric form,

the proportions tending towards'a reversal.

Temperatures and time of treatmentmay be varied to a considerable extent; treatment temperature from its highest point over an latter is to ordinary sandpaper,

- given sample of garnet fabric, thecoating of I I have discovered, however, thatif the garnet are changed in an unexpected manbecome harder,

serve the crystalline at .a low temperature to improve capillarity r the new product has some of the iron in the at a lower range of roasting temperatures s TREATMENT or GARNET Y Application filed September 22, 1930. been mi. 488,768.

over a-longer period of time being comparable with roasting over ashorter period of time at higher *temperatures. Satisfactory results may be attained by gradually lowering'the extended period of time,'or quickly reducing. the temperature at the end of the period of treatment to secure a desirable tempering. Continued treatmentat temperatures of approximately 1000 C. and above, however appears to have a detrimentallreactionary efi'ect, the material tending to lose its crystalline structure and'to break down, approaching an amorphous condition. Exhaustive work tests demonstrate that roasted garnet fabric, paperor cloth, is as superior tounroasted garnet fabric as the whether apa closed coat or in an open coat. A

plied in which has been roasted, whether used on a belt or'dr sander or otherwise, shows a capacity to. a rade approximatelytwice the area as untreated garnet. The retention of the grains y the bond is further improved, the hardness and sharpness of the grains and consequent cutting efiiciencyis increased, and the useful life of the garnet fabric in service is prolonged.

I claim:- v A 1. As'anabrasive, crushed garnet heated at sufficiently high temperature over a sufliciently extended period of time to convert a portion of the iron in ferrous form into the ferric form, tochange the color to a; deeper red and to increase the hardness.

'2: Method of producingan abrasive, which comprises roastmggarnet at a temperature sufliciently high'and for a period of time sufficiently long to increase the ferric content of the garnet, said temperature and time being maintained sufliciently low and short to prestructure of the garnet.

3. As an abrasive, crushed garnet roasted for a period of time varying from 4 to 16 hours, said garnet being characterized by a .darker c'olor,'and a harder and sharper grain at a temperatureof-fromf400. C. to 950 C. '95 '1 i.

prove the hardness and sharpness of the grain, which comprises roasting crushed garnet grains for a period of from 4 to 16.hours andat temperatures ranging from 4:00- C.

to 950 C.

In testimony w he'reof I- have hereunto subscribed my name.

EDWIN ,W. COLT. 

